JPS647332B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for measuring force acting during an impact test.

Impact testing is commonly used to measure the toughness of materials, and the method and test specimens are standardized in many countries (e.g. ASTM E370,
DIN51222). It is also common practice to measure and record the forces acting on the specimen during impact (CETurner, Measurement of Fracture Toughness by Instrumental Impact Testing).
Fracture Toughness by Instrumented Impact
Testing), Impact Testing of Metals, ASTM STP466,
American Society for Testing and Materials, 1970, pp. 93-114: Instrumental Impact Testing, ASTM STP563, American Society for Testing and Materials, 1974).

Test results are often expressed as force-time diagrams or force-displacement diagrams. It is also commonly known that the dominant force is observed when the hammer first strikes the specimen because the mass of the specimen must be accelerated to the speed of the hammer. This force is inevitable and occurs even if the specimen is simply supported and allowed to fly away. It has been observed that only inertial loads can fracture brittle specimens (J. C. Radon and C. E. Turner, Fracture Toughness Measurements by Instrumental Impact Testing).
Instrumented Impact Test)”, Engg.Fracture
Mech.Vol.1, pp. 411-428, 1969).

This inertial force peak causes the test and load transducer to vibrate very quickly, so that the force measured from the instrument tap is less than the true force acting on the specimen during approximately the first 20 to 30 microseconds. Do not give a value equivalent to . Brittle specimens often fail during this initial period, but in this case the inertial loading action completely masks the true failure load and the true energy expended in the failure process (the energy expended is usually equal to the force − It is determined by integrating the area in the displacement diagram, and it is almost impossible to separate the fracture energy from the energy consumed only for acceleration of the specimen).

For the meaning and effects of inertial loads, see H. J.A. Saxton (HJSaxton), Day.
R. Ireland (DRIreland) and D.A. L. Analysis and Control of Inertial Effects during Equipment Shock Testing (WLServer)
"During Instrumented Impact Testing", ASTM STP 563, American Society for Testing and Materials, 1974, pp. 50-73.

The vibrations caused by inertial loads are shown in FIG. In FIG. 1, a plurality of events at the start of impact are also schematically shown. Code 0 in the diagram
At this point the tap touches the specimen and begins to accelerate it. At time 1, the center of the specimen reaches the speed of the hammer and the force reaches a first peak. As the specimen and tap are compressed during acceleration, the specimen bounces and the force decreases after point 1. At the same time, the specimen begins to bend and a reaction force begins to appear on the support. The bending of the specimen rapidly dissipates the extra kinetic energy of the specimen, and the tap delivers a second blow to the specimen at the beginning of time point 2. Since the speed difference at this time is relatively small, the force generated by acceleration is relatively small. The same process of striking and releasing is repeated several times with decreasing force amplitude, and the forces are summed to form the actual bending force. A very detrimental effect of the inertial load acting on the notch of the specimen is the possible interference with the fracture initiation process at the bottom of the notch. High inertia load peaks generate complex stress waves across the notch, and according to Seifert et al.
This effect can cause a reduction in failure load of approximately 20% (K. Seifert).
Seifert) and El Davrill Mayer (L.
W. Meyer) “Mo¨glichkeiten zum”
Verminder des Aufschlagimpulses bei
Bruchza¨higkeit−spru¨fungen unter
schlagartiger Beansprü¨chung”,
Materialpru¨f.19, Nr.6, June 1977). These researchers conducted unpublished finite element calculations (finite−
``element calculations'' and predicts a similar effect. These results may partially explain why the correlation between Sharpie V-notch impact energy and other toughness measurements is relatively poor.

Since it is clear that the force measured by the tap does not give reliable results at the first moment of impact, several methods have been proposed to avoid inertial loading effects. One solution is to measure bending moments directly from the specimen by equipping it with strain gauges. This method is time consuming and expensive, and is not applicable to low or high temperature tests. A method of determining the bending force from the elapsed time before the specimen breaks has also been proposed. This indirect method is based on the knowledge that bending force depends approximately linearly on time. A disadvantage of this method is that the moment at which the specimen breaks must be measured very precisely, and this measurement can only be made by instrumenting the specimen. The most widely used method is to slow the impact velocity. Slower speeds reduce vibrations and facilitate analysis of force-time diagrams. However, on the other hand, some of the dynamic nature of the test will be lost. The effective energy is reduced and therefore the velocity is further reduced while the specimen is bent, which increases the variability of the test results.

The effect of inertial loads can also be removed from the tap by attaching the specimen to a movable hammer. This method has been found to be effective by many researchers. FIG. 2 shows an actual force-displacement diagram for an aluminum Sharpy V-notch specimen (solid line). The dotted line in FIG. 2 was obtained when a similar specimen was attached to a hammer. The first inertia peak is avoided and the vibrations are also relatively small. This means that the inertial load is acting on two supports, that its size is halved because it is divided between both supports, and that the vibrations to be reduced are This is explained by the time it takes to reach the measurement tap. This method is the only method that also eliminates harmful stress waves across the notch, and therefore provides more reliable results. However, it is practically impossible to use this method at temperatures other than room temperature.
This is because it takes time to attach the test piece, and even if it is possible to attach a very cold or hot test piece, it is not possible to know the temperature of the test piece at the moment of the actual impact.

It is an object of the present invention to provide a method and apparatus for reducing inertial loading effects in impact tests and changing the stress state in the specimen towards three-point bending, thereby allowing a more reliable analysis of the data. That's true.

That is, in the impact test method of the present invention, a bending test piece having a notch is supported on at least one surface thereof, and the impact toughness of the bending test piece is tested by applying a blow to a surface different from the supporting surface. In the method of It is characterized by giving.

Furthermore, the impact testing apparatus of the present invention includes a stand equipped with a device for horizontally supporting a bending test piece having a cutout portion by supporting the test piece on at least one surface thereof; In the apparatus for testing the impact toughness of the bending specimen, which comprises a movable hammer that strikes a surface, the supporting device comprises a fixed tap that supports the specimen at the middle of the specimen on the opposite surface from the notch of the specimen. , the hammer has two striking blades spaced apart from each other, and the hammer is configured to strike the test piece simultaneously at two points located on the face of the notch and on both sides of the middle part. It is characterized by being movable.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. 3 to 5 show a device according to the invention, in which a hammer 3 is attached to a rod 7 and pivoted to the upper part of an impact stand 6.
The hammer 3 and the rod 7 form a pendulum which can be swung about a pivot from an upper starting position 3a to a lower striking position 3b. The details of the device for holding the hammer in the upper position are the same as those of conventional devices, and are therefore not shown.

The test specimen 1 is placed in a horizontal position on a flat plate 5 provided at the bottom of a stand 6, such that the notch-like cutout provided in the test specimen is substantially vertical. The middle part of the test piece on the opposite side of the test piece from the notch is supported by a fixing tap 2. This tap 2 is shaped to come into contact with the test piece along a vertical line on the same vertical plane of the test piece as the notch.

The hammer 3 has two striking blades 4 spaced apart from each other, and is capable of simultaneously striking the test piece at two points located on the face of the notch and on both sides of the middle part of the test piece 1. The specimen 1 is thus bent around the fixed tap 2. Tap 2 is equipped with a device for measuring the force acting on the specimen during impact.

The present invention combines the advantages of the conventional shear pie test and the method of hammer mounting the test specimen. This can be done by reversing the geometry from the conventional one. That is, by simultaneously striking both ends of the stationary test piece 1 with a hammer 3 equipped with two striking blades 4, the test piece 1 is bent around the stationary fixing tap 2. The specimen is only supported, for example on a flat plate 5, and is therefore free to deform in the bending plane A-A. The fourth section is a cross-sectional view taken along the line of FIG.
In the figure, starting position 3a and impact position 3b
A hammer is shown. The force can be measured from tap 2. In this design,
The inertial load action mainly acts on the striking blade 4, and only reduced vibrations are transmitted to the middle part of the test specimen. What is very important here is that there are no inertial loads acting across the notch and therefore no extra stress waves in this notch. It must be emphasized here that published calculations of stresses at the bottom of the notch do not account for the effects of extra transverse stress waves, and therefore the novel configuration of the present invention is not included in the general analysis. This means that it gives a stress state at the bottom of the notch that is closer to the stress state estimated by the method.

The tap 2 can also be modified to consist of two supporting tips that are adjacent to each other with a slight distance from each other and are arranged symmetrically with respect to the test specimen notch. Such a modification would change the test geometry from a three-point bend to a four-point bend. Also, since the middle portion of the specimen 1 remains relatively stationary during the test, the specimen may be equipped with some type of notch opening gauge. Furthermore, since there is no need to attach a test piece, the test can be performed at a variety of different temperatures, similar to the conventional Charpy test. The tester simply places the specimen symmetrically and positions it so that both ends of the specimen are struck simultaneously. Such alignment of the test piece can be easily performed using a positioning device.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram in the prior art showing vibrations caused by inertial loads and events that occur at the start of impact. FIG. 2 is a force-displacement diagram of an aluminum sharpie V-notch specimen (solid line) and the specimen attached to a hammer (dotted line). FIG. 3 is a front view of the device according to the invention. FIG. 4 is a sectional view taken along line B-B in FIG. 3, showing the upper and lower positions of the hammer.
FIG. 5 is a sectional view taken along line A-A in FIG. 3. 1... Test piece, 2... Fixing tap, 3... Hammer, 4... Hitting blade, 5... Flat plate, 6... Stand, 7... Rod.

Claims (1)

[Claims] 1. A method of testing the impact toughness of a bending test piece by supporting a bending test piece having a notch on at least one surface and applying a blow to a surface different from the supporting surface. In this step, the test piece is supported at the middle part of the test piece on the opposite side to the notch part, and the test piece is simultaneously struck at two points located on the face with the notch part and on both sides of the middle part. An impact test method characterized by: 2. Said test specimen is placed in a horizontal position, the cutout is oriented substantially vertically, the support of the middle part of the test specimen is oriented substantially horizontally, and the striking movement is substantially horizontal at the moment of striking. 2. A method according to claim 1, wherein the support is applied in a direction opposite to the direction of said support. 3. The method of claim 2, wherein the test piece is supported along a vertical line in the same vertical plane of the test piece as the notch. 4. The method according to claim 1, wherein the force acting on the test piece is measured at the intermediate portion that supports the test piece. 5. A stand equipped with a device for horizontally supporting a bending test specimen having a notch on at least one surface thereof, and a movable hammer for striking a surface of the test specimen different from the supporting surface. In the apparatus for testing the impact toughness of the bending specimen, the supporting device comprises a fixing tap that supports the specimen at the middle of the specimen on the opposite side of the notch, and the hammers are spaced apart from each other. The hammer has two striking blades arranged together, and the hammer is movable so as to simultaneously strike the test specimen at two points located on the face of the notch and on both sides of the intermediate part. An impact test device featuring: 6 the tap is placed at the bottom of the stand;
6. The apparatus of claim 5, wherein said hammer is pivoted in the form of a pendulum and is pivotally mounted on the top of said stand. 7. The tap has a shape that contacts the test piece along a vertical line on the same vertical surface of the test piece as the notch, and a flat plate member that horizontally supports the test piece is arranged at the bottom of the stand. The device according to scope item 6. 8. The device according to claim 5, wherein said tap is provided with two support tips adjacent to each other and located symmetrically with respect to said notch. 9. The device according to claim 5, wherein the tap is provided with a force measuring device.